1. Field of Invention
The present invention relates to a power converter. More particularly, the present invention relates to a power converter with stable voltage gain and method.
2. Description of Related Art
Wireless power transfer technology has been applied in many fields, such as electric cars, consumer electronics products, etc. The wireless power transfer technology enables the power transfer based on the electromagnetic induction principle.
Reference is made to FIG. 1A. FIG. 1A is a schematic diagram of a power converter 100 used in some approaches. As shown in FIG. 1A, the power converter 100 used in some approaches includes a transformer 120, a full bridge inverter circuit 140 and a bridge rectifying circuit 160. The transformer 120 is formed by the primary winding Ns and the secondary winding Ns, and the mutual inductance of these windings is M. The inductance value of the primary winding is L1 (which is referred to as primary inductor hereinafter), and the inductance value of the secondary winding is L2 (which is referred to as secondary inductor hereinafter). The full bridge inverter circuit converts the DC input voltage to the AC voltage VAC, and transfer the AC voltage VAC to the transformer 120 and the bridge rectifying circuit 160, so as to generate the DC output voltage VDcout. Further, the transformer 120 may have a larger leakage inductance with the larger air gaps between the primary winding Np and the secondary winding Ns. To compensate the leakage inductance of the transformer, the power converter 100 used in some approaches further includes a primary side compensation capacitor Cp and a secondary side compensation capacitor Cs.
Reference is made to FIG. 1B to FIG. 1E. FIG. 1B is a graph illustrating the relationship of the voltage gain AV of the power converter 100 with different load and the operating frequency. FIG. 1C is a graph illustrating the relationship of the input impedance of the power converter 100 with different load and the operating frequency. FIG. 1D is a graph illustrating the relationship of the voltage gain Av of the power converter 100 with different coupling factors k and the operating frequency. Further, FIG. 1E is a graph illustrating the relationship of the input impedance of the power converter 100 with different coupling factors k and the operating frequency. The operating frequency in FIG. 1B to FIG. 1E is the ratio of the operating frequency fo of the power converter 100 and the resonant frequency corresponding to the primary inductor L1 and the primary side compensation capacitor Cp. The voltage gain Av in FIG. 1B and FIG. 1D is the ratio of the DC output voltage Vdc,out and the DC input voltage Vin in FIG. 1A. Req in FIG. 1C and FIG. 1E refers to the ratio of the imaginary part and the real part of the input impedance of the power converter 100.
As shown in FIG. 1B to FIG. 1E, in general, the operating frequency fo of the power converter 100 is set to be equal to the resonant frequency of the primary inductor L1 and the primary side compensation capacitor Cp, so that the input impedance is pure resistance, and the reactive power is thus reduced. However, the voltage gain Av of the power converter 100 deviates greatly with different loads or deviation of the coupling factor k, and thus the voltage between the internal circuits changes greatly. As a result, elements withstanding high voltage are utilized, and costs of the power converter rise. In addition, the deviation of the voltage gain of the power converter also makes an impact on the conversion efficiency of the power converter.
Therefore, a heretofore-unaddressed need exists to address the aforementioned deficiencies and inadequacies.